This invention relates to acoustical insulation material, and is particularly concerned with the production of an efficient muffler material especially adapted for automobile mufflers, which has improved properties of high temperature, vibration and chemical resistance, and which retains its structural configuration and rigidity to the hostile environment of automobile heat, vibration, and the gas pressures of automobile exhaust systems, over long periods of operation without substantial reduction in acoustical properties and without degradation or adverse affect on muffler performance.
Resin impregnated glass fiber insulation currently employed on automobile mufflers has the disadvantage of not being capable of withstanding muffler temperatures up to 1,500.degree. F. Thus, automobile muffler materials presently employed generally have an upper temperature limit of the order of about 350.degree. F.
U.S. Pat. No. 1,832,571 discloses a sound absorbing material formed of felt coated with granular particles such as pumice and a suitable binder such as casein glue.
U.S. Pat. No. 2,731,359 discloses a refractory fiber body formed of refractory fibers of alumina and silica coated with a silicon metal binder which is introduced into the fibrous body in the form of a slurry of fluid suspension in a suitable liquid medium, followed by firing at high temperatures in a non-oxidizing atmosphere of nitrogen or carbon monoxide to form a refractory inorganic silicon nitride or silicon carbide bond.
U.S. Pat. No. 3,359,717 discloses fibrous blends, particularly intimate cardable blends of inorganic fibers such as asbestos fibers and glass fibers, and including a drag agent such as colloidal silica to overcome the slipperiness of the fine glass particles. In addition to asbestos fibers, other inorganic fibers of a length too short to card, such as alumino-silicate fibers, are employed together with the fine glass fibers. The addition of the drag agent or colloidal silica is achieved by directing a spray of the liquid material over the fibers.
U.S. Pat. No. 3,002,862 discloses inorganic compositions comprising clay particles coated with a layer of silica, produced by mixing colloidal silica with a finely divided clay such as China clay, to form an electrically conductive composition.
U.S. Pat. No. 3,573,123 and 3,579,401 relate to high temperature resistant materials such as tapes containing carbon and silica, fabricated in cylindrical layers.
It is an object of the present invention to provide an efficient muffler material having good sound absorption characteristics, a particular object being the provision of a muffler material for automobiles which will withstand high temperatures of the order of 2,000.degree. F while maintaining its structural integrity under vibration and in the presence of exhaust gas pressures and corrosive chemical components in the exhaust gas, over an extended period of operation, the muffler material being readily fabricated and being relatively inexpensive.